The present invention relates to a method and a circuit arrangement for determining a quality level of phase signals, in particular in the detection of a motion or an angle of rotation or a torque on axes or shafts.
For example, to detect the torque acting on a steering wheel axis of a motor vehicle while the steering wheel rotates, very small angular changes must be measured in both directions of rotation of the steering wheel. It is possible to use incremental angle sensors in this case that assign a measured phase value to an angular position based on the evaluation of signals that are optical, magnetic or that are produced in any other way, e.g., by the rotation, and that are detected using suitable means. To increase the unambiguous range, it is possible to look at a further measurement channel with a different phase slope. A plurality of measured phase values is therefore obtained in this case, from which the quantity to be measured, such as the angle of rotation, an angular difference or the distance from a target, is to be determined.
When more than two phase signals are involved, a method described in publication DE 101 42 449 A1, for example, is used to evaluate measured phase values of this type. In that method, a highly exact, robust and unambiguous measured phase or angle value is produced from a number N of multivalued, disturbed phase signals. To accomplish this, the measured phase values are mathematically transformed using a linear transformation method, among other things, and evaluated with a specified weighting.
The method is used, e.g., with an optical angle sensor, in the case of which N parallel tracks are created on a cylinder. Located on each of the N tracks (i=1 . . . N) are ni periods of a phase information that, in the optical case, for example, is represented by ni periods of light-dark transitions. Other sensor principles, e.g., magnetic or capacitive, are also possible in this case. The tracks of the sensor can also be created on a plane instead of a cylinder, e.g., in the case of a path sensor.
It is also known, from publication DE 195 06 938 A1, that the phase signals can be evaluated via the single or multiple application of a classical or modified vernier principle.
To determine an angular difference, it is furthermore also known from publication DE 101 42 448 A1 that the measured phase values are summed in a weighted manner and, from this sum, the whole-number portion and the non-whole number portion are determined. The non-whole number portion is proportional to the angular difference between two groups of tracks of an incremental-value indicator on a shaft. The torque acting on the shaft can therefore be determined via multiplication with the spring rate of a torsion bar installed between the groups of tracks.
It is also known per se from publication DE 100 34 733 A1 that a specified offset value is added to the measured phase value in an initialization phase and, in turn, as a result, the offset value is compensated. An iterative approximation method carried out to perform offset compensation of two orthogonal sensor signals is also known per se from publication DE 199 15 968 A1.
The method according to the general class can be used, for example, with a corresponding sensor arrangement—as described in publication DE 101 42 448 A1 above—on the steering shaft of a vehicle as a “torque angle sensor” (TAS) that simultaneously transmits the steering angle and steering torque.